1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor device using a wafer having a large diameter.
2. Description of the Prior Art
Generally, a wafer having a diameter below 30mm.phi. is used for manufacturing such semiconductor devices as a semiconductor discrete device and a semiconductor integrated circuit. Recently with the advance of semiconductor technology, a wafer having a large diameter as 50mm.phi. or 70mm.phi. begins to be adopted. In the usual manufacturing of semiconductor devices, a thickness such as 230.mu., 280.mu., 330.mu., 380.mu. of the wafer is necessary corresponding to the diameter 40mm.phi., 50mm.phi., 60mm.phi., 75mm.phi. of the wafer respectively.
On the other hand, in the manufacturing process, it is necessary to handle the wafer with some tools, and the handling is usually made at the peripheral portion of the wafer. Accordingly, the stress applied to the wafer is increased in proportion to the diameter thereof, which often causes its mechanical destruction. Furthermore, for instance, in the manufacturing of semiconductor controlled rectifier (S.C.R.)consisting of four regions whose impurity type is alternatively different, the thickness of cathode, gate and anode regions are predetermined in characteristics regardness of the thickness of the wafer. Therefore, the middle region thereof becomes thick, which makes the forward characteristics low compared to a semiconductor device made of the 30mm.phi. wafer having a 160.mu. thickness. Considering mechanical strength, the thickness of the wafer having 40mm.phi. to 75mm.phi. is desired to be above 230.mu., and considering forward characteristics, the thickness is desired to be about 160.mu.. However, practically, a 180mm.phi. wafer is used at the sacrifice of the forward characteristics and mechanical strength.
As above-mentioned, the large diameter tendency of the wafer brings an elimination of labor, however, in the other side, causes the lowering of the characteristics.